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PDF MAX1774 Data sheet ( Hoja de datos )
| Número de pieza | MAX1774 | |
| Descripción | Dual / High-Efficiency / Step-Down Converter with Backup Battery Switchover | |
| Fabricantes | Maxim Integrated | |
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19-1810; Rev 1; 1/02
EVAALVUAAILTAIOBNLEKIT
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
General Description
The MAX1774 is a complete power-supply solution for
PDAs and other hand-held devices. It integrates two
high-efficiency step-down converters, a boost converter
for backup battery regulation, and four voltage detec-
tors in a small 32-pin QFN or 28-pin QSOP package.
The MAX1774 accepts inputs from +2.7V to +28V and
provides an adjustable main output from 1.25V to 5.5V
at over 2A. The secondary core converter delivers an
adjustable voltage from 1V to 5V and can deliver up to
1.5A. Both the main and core regulators have separate
shutdown inputs.
When the AC adapter power is removed, an external P-
channel MOSFET switches input to the main battery.
When the main battery is low, the backup step-up con-
verter sustains the main output voltage. When the back-
up battery can no longer deliver the required load, the
system shuts down safely to prevent damage. Four on-
board voltage detectors monitor the status of the AC
adapter power, main battery, and backup battery.
The MAX1774 evaluation kit is available to help reduce
design time.
________________________Applications
Hand-Held Computers
PDAs
Internet Access Tablets
POS Terminals
Subnotebooks
Pin Configurations
TOP VIEW
GND
GND
MDRV
PGNDC
PGND
NDRV
CVL
IN
PDRV
CVH
1
2
3
4
5
6
7
8
MAX1774
24 ACO
23 INC
22 GND
21 FBC
20 CS-
19 CS+
18 FBM
17 N.C.
GND GND
Features
o Dual, High-Efficiency, Synchronous-Rectified
Step-Down Converters
o Thin, Small (1mm High) QFN Package
o Step-Up Converter for Backup Battery
o Main Power
Adjustable from +1.25V to +5.5V
Over 2A Load Current
Up to 95% Efficiency
o Core Power
Adjustable from 1V to 5V
Internal Switches
Up to 1.5A Load Current
Up to 91% Efficiency
o Automatic Main Battery Switchover
o 100% (max) Duty Cycle
o Up to 1.25MHz Switching Frequency
o Input Voltage Range from +2.7V to +28V
o Four Low-Voltage Detectors
o 170µA Quiescent Current
o 8µA Shutdown Current
o Digital Soft-Start
o Independent Shutdown Inputs
Ordering Information
PART
MAX1774EEI
MAX1774EMJ
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 QSOP
32 7mm x 7mm QFN
Functional Diagram
AC
ADAPTER
MAIN
BATTERY
BACKUP
BATTERY
MAX1774
MAIN (+3.3V)
CORE (+1.8V)
AC OK
LOW MAIN BATTERY
DEAD MAIN BATTERY
32 7mm x 7mm QFN
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS (continued)
(Figure 1, VIN = VINS = +12V, VINC = VCS- = VCS+ = +3.3V, VCORE = +1.8V, TA = 0°C to +85°C, unless otherwise noted. Typical values are
at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
SHDNM, SHDNC Input Low
Current
SHDNM = SHDNC = GND
-1 1 µA
SHDNC Input High Current
SHDNM Input High Current
VSHDNC = +5.5V
VSHDNM = +5V
5 µA
2 25 µA
ELECTRICAL CHARACTERISTICS
(Figure 1, VIN = VINS = +12V, VINC = VCS- = VCS+ = +3.3V, VCORE = +1.8V, TA = -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER
Input Voltage
Input Quiescent Supply Current
CS- Quiescent Supply Current
Core Regulator Quiescent
Supply Current
Backup Mode BIN Quiescent
Supply Current
IN Shutdown Supply Current
MAIN REGULATOR
Main Output Voltage Adjust
Range
FBM Regulation Threshold
FBM Input Current
Current-Limit Threshold
Minimum Current-Limit
Threshold
Valley Current Threshold
Zero Current Threshold
PDRV, NDRV Gate Drive
Resistance
CS- to CVL Switch Resistance
Maximum Duty Cycle
Minimum On-Time
Minimum Off-Time
SYMBOL
VIN
IIN
CONDITIONS
VFBM = +1.5V, VFBC = +1.5V, VSHDNM =
VSHDNC = +3.3V
ICS-
VFBM = +1.5V, VFBC = +1.5V, VSHDNM =
VSHDNC = +3.3V
IINC
VFBM = +1.5V, VFBC = +1.5V, VSHDNM =
VSHDNC = +3.3V
VBIN = +3.3V, CS- open
IBIN VFBM = +1.5V, VSHDNM = +3.3V,
VBKOFF = +1.5V, SHDNC = GND
SHDNM = SHDNC = GND
VFBM
IFBM
V(CS+ - CS-) = 0 to +60mV,
VIN = +3.5V to +28V
VFBM = +1.3V
VCS+ - VCS-
VCS+ - VCS-
VCS+ - VCS-
VCS+ - VCS-
VCS- = +3.3V, IPDRV, INDRV = 50mA
ICVL = 50mA
MIN
2.7
1.25
1.21
-0.1
60
5
40
0
100
200
200
MAX UNITS
28 V
40 µA
220 µA
105 µA
110 µA
40 µA
5.5
1.29
0.1
100
25
60
15
5.5
9.5
650
650
V
V
µA
mV
mV
mV
mV
Ω
Ω
%
ns
ns
_______________________________________________________________________________________ 5
5 Page 
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Pin Description (continued)
PIN
QSOP QFN
— 10
13 11
14 12
15 13
16 14
17 15
18 16
—
17, 25,
29
19 18
20 19
21 20
22 21
23 22
24 23
25 24
26 26
27 27
28 28
NAME
LXB2
BIN
BKOFF
ACI
DBI
LBI
REF
N.C.
FBM
CS+
CS-
FBC
GND
INC
ACO
LBO
INS
LXC
FUNCTION
Backup Converter Switching Node. Connect LXB2 to LXB as close to the IC as possible.
Backup Battery Input. Connect BIN to the output of the backup boost regulator. Bypass BIN with a 10µF or
greater capacitor to GND. When the MAX1774 is in backup mode, BIN powers the main output.
Backup Disable Input. Driving BKOFF below +0.5V disables the backup mode. In backup mode, the
device enters shutdown when this pin is pulled low. BKOFF can be driven from a digital signal or can be
used as a low battery detector to disable the backup converter when the backup battery is low.
AC Adapter Low-Voltage Detect Input. Connect to adapter DC input. When the voltage at ACI falls
below the voltage at INS plus +0.22V, ACO asserts.
Dead Battery Input. Connect DBI to the main battery through a resistive voltage-divider. When DBI drops
below +1.20V, no AC adapter is connected (ACO is low, but main output still available), BKUP asserts.
Low-Battery Input. Connect LBI to the main battery through a resistive voltage-divider. When the
voltage at LBI drops below +1.20V, LBO asserts.
Reference Voltage Output. Bypass REF to GND with a 0.22µF or greater capacitor.
No Connection. Not Internally Connected.
Main Output Feedback. Connect FBM to a resistive voltage-divider to set main output voltage
between +1.25V to +5.5V.
Main Regulator High-Side Current-Sense Input. Connect the sense resistor between CS+ and CS-.
This voltage is used to set the current limit and to turn off the synchronous rectifier when the
inductor current approaches zero.
Main Regulator Low-Side Current-Sense Input. Connect CS- to the main output.
Core Output Feedback. Connect FBC to a resistive voltage-divider to set core output between +1.0V
to +5.0V.
Analog Ground
Core Supply Input
Low AC Output. Open drain ACO asserts when ACI falls below the main output voltage plus 0.22V.
Open-Drain Low-Battery Output. LBO asserts when LBI falls below +1.20V.
Power-Supply Input Voltage Sense Input. Connect INS to the power-supply input voltage.
Core Converter Switching Node
Detailed Description
The MAX1774 dual step-down DC-DC converter is
designed to power PDA, palmtop, and subnotebook
computers. Normally, these devices require two sepa-
rate power supplies–one for the processor and another
higher voltage supply for the peripheral circuitry. The
MAX1774 provides an adjustable +1.25V to +5.5V main
output designed to power the peripheral circuitry of
PDAs and similar devices. The main output delivers up
to 2A output current. The lower voltage core converter
has an adjustable +1.0V to +5.0V output, providing up
to 1.5A output current. Both regulators utilize a propri-
etary regulation scheme allowing PWM operation at
medium to heavy loads, and automatically switch to
pulse skipping at light loads for improved efficiency.
Under low-battery conditions, the MAX1774 enters
backup mode, making use of a low-voltage backup
battery and a step-up regulator to power the output.
Figure 1 is the MAX1774 typical application circuit.
Operating Modes for the
Step-Down Converters
When delivering low output currents, the MAX1774 oper-
ates in discontinuous conduction mode. Current through
the inductor starts at zero, rises as high as the minimum
current limit (IMIN), then ramps down to zero during
_______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet MAX1774.PDF ] | |
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